Oxide ores and concentrates can have metallurgical properties complicating valuable metal recovery by hydrometallurgical processes, particularly by aqueous leaching processes. The recovery of silver from silver-containing ores having base metals, such as for example lead, and zinc, among others, can be complicated when the both of the silver and base metals are brought into solution during the leaching process.
Furthermore, some aqueous leaching processes can be expensive and can potentially present a severe environmental hazard if not properly controlled. For example, in direct cyanide leaching, cyanide is contacted with the ore or concentrate in the presence of molecular oxygen to dissolve the valuable metal and form a pregnant leach solution. Activated carbon can be employed to collect the dissolved valuable metal. Although effective, cyanide leaching can be expensive and, if not properly controlled, is extremely hazardous.
In another process, the ore or concentrate is contacted with a hot agitated chloride lixiviant. A typical lixiviant solution includes about 200 g/L sodium chloride, 10 g/L ferric iron, and 10 g/L HCl. The lixiviant dissolves not only silver but also lead, zinc, tin, and other base metals. Separation of the various dissolved metal species can be expensive and difficult. Additional expense is incurred by the use of an acidic solution containing hydrochloric acid and elevated process solution temperatures. Moreover, the elevated temperature and high hydrochloride acid concentration present an environmental hazard.